In general, metal or semiconductor colloid (ultra fine particle) is an important industrial material which is broadly used in various fields, for example, medical treatment [as a medicine (medicine of ultra fine particles having penetrating ability to membrane internus), various inspection agents or DDS], dye (coating), foods or catalyst. Especially, metal particles of several tens to several hundreds nano meter size (called as submicron: meso size) and having narrow distribution is expected as a high functional materials such as diagnostic which uses Raman spectrum or microwave or a labeling agent for electron microscope.
For example, Assay method, which uses colloidal metal particles has been developed. Said method is characterized as follows. That is, since colloidal metal is used as a label, the specific bonding site to be labeled is bonded on colloidal metal by absorption and said labeling material is detected and measured (JP Laid Open Publication 6-116602, hereinafter shortened to Document A).
The principle can be illustrated as follows. That is, it becomes well known that the ultra fine particles can enhance the resonance Raman scattering by a surface sensitizing effect (Surface Enhanced Raman Scattering, Surface Enhanced Resonance Raman Scattering; SERRS), further, it is found out that colloidal metal displays said signal sensitizing effect, therefore, the special characteristics of said colloidal metal is utilized.
As mentioned above, when colloidal metal which displays above mentioned effect to Raman rays is used as the labeling agent, various detecting subject which reacts with colloidal metal, for example, an antibody or a ligand can be detected using above mentioned effect. Sill more, it is possible to detect the subject to be detected using Raman ray in good sensitivity by bonding a material having a specific bonding site or a Raman sensitizing substance (i.e. colloidal metal) to said subject to be detected, in other word, since by treating a Raman sensitizing substance with an intervening molecule, said substance becomes to have an ability to bond with the subject to be detected, it becomes the labeling material to the subject to be detected.
However, these conventional ultra fine particles of metal is maintaining it's dispersing state by the repulsing forth of surface ions in the medium such as water, therefore, when the substance having opposite electric charge exists, said ultra fine particles of metal are neutralized and cohered, that is, the instability is pointed out as the problem.
In the meanwhile, in above mentioned Document A, the art to prepare a stable sol which does not cause cohesion easily with salt or acid by coating a sol of gold with alkane thiol or thiol derivatives (called as protection or modification) is disclosed. However, the disclosed method for producing is complicated and the obtained sol cannot be said as the monodispersed particles, namely, as the narrow distributed particles, further, the size of obtained particles is relatively larger, therefore, the improvement of an ability is required when used as a detecting reagent.
For the purpose to dissolve said problem and to obtain a dispersion of metal fine particles having various improved characteristics, the method to improve the dispersion stability of metal fine particles based on the repulsing forth of the carried PEG is disclosed [for example, W. P. Wuelfing et al. J.Am.Chem., Soc.120 (48), 12696–12697 (1988)]. Said method can be illustrated as follows, namely; using a polymer having water soluble structure like to polyethyleneglycol (PEG), having high mobility and possessing a functional group which has affinity to metal fine particles on one end, and by loading this polymer to metal fine particles.
However, considering metal fine particles used for a diagnostic, when polymer having PEG structure is loaded on the surface of metal fine particles, although the dispersion stability is improved, the use of it is quite limited because it lacks a reactive group with a group which an antibody has (a group of peculiar reactivity, a group reacts with the group which subject to be detected has).
Aiming to dissolve above mentioned various problems, the inventors of the present invention have already proposed a novel stabilized dispersion complex [48th Polymer Forum (1999) held on October 6–8, at Niigata Univ. Igarashi Campus (Abstract of Polymer Society) Vol.48, No.14, 4113–4114, published on Sep. 20, 1999]. Said novel complex is prepared by synthesizing PEG derivative to one end of which (for example, α-end) a functional group which can load ultra fine particles of metal, metal oxide or semiconductor (for example, mercapt group or polyamine group) is introduced and to another end (ω-end) a functional group which can react with a functional compound i.e., antibody, protein or dye, PEG to which said functional groups are introduced is loaded on ultra fine particles of metal, metal oxide or semiconductor so as to improve the dispersion stability of said ultra fine particles, that is, said novel complex possesses a functional group having reactivity with a functional compound on another end of the PEG chain which spreads (extends) from the surface of ultra fine particles.
In said document, the process to make exist polymer derivatives (called as a polymer modifying agent) having above mentioned PEG structure in the process to produce dispersion of colloidal particle from auric acid chloride and sodium borohydride (NaBH4) as a reducing agent is not discussed. Further, the gold sol particles obtained by the conventional art is far from the monodispersed colloidal particle, still more, is not of satisfying quality from the view point of dispersion stability.
Further, there is no experimental report to prepare ultra fine particles of semiconductor in the presence of polymer derivatives having same PEG structure. The object of the present invention is to improve the defects of above mentioned conventional arts, and is to provide monodispersed fine particles (colloidal particles, nano size particles) of metal such as gold, platinum, silver or rhodium or semiconductor such as CdS, ZnS, CdSe, ZnSe or InAs whose dispersion stability is improved, that is, the dispersion of fine particles whose particle size is uniform and relatively small. Further, the dispersion of fine particles of gold or others (colloidal particles), whose dispersion stability is improved, possesses a block polymer of a graft polymer having a PEG chain or a PEG unit on the surface layer, and by introducing above mentioned functional group to the voluntary ends of said chain or polymer the functions of said functional groups have are provided to the dispersion. Another object of the present invention is to provide a method for producing of above mentioned dispersion.
The inventors of the present invention have carried out intensive study to dissolve above mentioned problem and investigated the reaction system which generate dispersion of metal fine particles (colloidal particles) by good reappearance and stable, and found out that the monodispersed fine particles (colloidal particles) whose dispersion stability is improved can be obtained by generating metal fine particles or semiconductor fine particles by reduction of auric acid chloride under the presence of specific compound (polymer) possessing above mentioned PEG unit, and dissolved above mentioned object.
Furthermore, the inventors of the present invention have found out that fine particles (colloidal particle) dispersion whose dispersion stability is remarkably improved can be obtained by adding block or graft polymer to the solvent of fine particles (colloidal particle) dispersion for gold which is on the market, and monodispersed metal fine particles (colloidal particle) having uniform and small particle size, in other words, of nano size showing quantum effect can be obtained only by mixing metal acid and said block or graft polymer (not necessary to add a reducing agent).